Dual cores for golf balls

ABSTRACT

The present invention is directed to a golf ball comprising a dual core component. The dual core comprises an interior center component formed from a thermoset material, a thermoplastic material, or combinations thereof. The dual core also comprises a core layer disposed about the center component, formed from a thermoset material, a thermoplastic material, or combinations thereof. The present invention golf ball may further comprise an outer core layer that surrounds the dual core. The resulting multi-layered golf ball of the present invention provides for enhanced distance without sacrificing playability or durability when compared to known golf balls.

CROSS REFERENCE TO RELATED APPLICATIONS

This application claims priority on U.S. patent application Ser. No.09/048,701 filed Mar. 26, 1998, which claims priority from U.S.provisional patent application Ser. No. 60/042,439 filed Mar. 28, 1997.

FIELD OF THE INVENTION

The present invention relates to golf balls and, more particularly, toimproved golf balls comprising a unique dual core configuration. Theimproved golf balls provide for enhanced distance and durabilityproperties.

BACKGROUND OF THE INVENTION

A number of two-piece (a solid resilient center or core with a moldedcover) and three-piece (a liquid or solid center, elastomeric windingabout the center, and a molded cover) golf balls have been produced. Thedifferent types of materials utilized to formulate the cores, covers,etc. of these balls dramatically alters the balls' overallcharacteristics. In addition, multi-layered covers containing one ormore ionomer resins have also been formulated in an attempt to produce agolf ball having the overall distance, playability and durabilitycharacteristics desired.

Despite the great number of materials and combinations of materialsutilized in prior art golf balls, there still remains a need for animproved golf ball exhibiting superior properties.

These and other objects and features of the invention will be apparentfrom the following summary and description of the invention, thedrawings and from the claims.

SUMMARY OF THE INVENTION

In one aspect, the present invention provides a golf ball comprising adual core comprising a center component and a core layer disposed aboutthe center component. The center component comprises a thermoplasticmaterial and the core layer comprises a thermoset material.

In yet another aspect, the present invention provides a multi-layer golfball comprising a dual core component that includes a center componentand a core layer disposed about the center component. The centercomponent comprises a thermoset material and the core layer comprises athermoplastic material.

In yet another embodiment, the present invention provides a multi-layergolf ball comprising a dual core, having a center component and a corelayer, both of which comprise a thermoplastic material.

BRIEF DESCRIPTION OF THE DRAWINGS

FIG. 1 is a cross-sectional view of a preferred embodiment golf ball inaccordance with the present invention illustrating a core and a covercomprising an inner layer and an outer dimpled layer;

FIG. 2 is a diametrical cross-sectional view of the preferred embodimentgolf ball depicted in FIG. 1 having a core and a cover comprising aninner layer surrounding the core and an outer layer having a pluralityof dimples;

FIG. 3 is a cross-sectional view of another preferred embodiment golfball in accordance with the present invention comprising a dual corecomponent;

FIG. 4 is a cross-sectional view of yet another preferred embodimentgolf ball in accordance with the present invention comprising a dualcore component;

FIG. 5 is a cross-sectional view of another preferred embodiment golfball in accordance with the present invention comprising a dual corecomponent and an outer core layer;

FIG. 6 is a cross-sectional view of yet another preferred embodimentgolf ball in accordance with the present invention comprising a dualcore component and an outer core layer; and

FIG. 7 is a schematic view of an assembly used for molding a preferredembodiment golf ball in accordance with the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

The present invention is directed to a golf ball comprising a dual-corecomponent. The present invention golf balls preferably utilize amulti-layer cover. However, the golf balls may instead utilizeconventional cover materials such as balata or blends of balata withelastomeric or plastic materials. The multi-layer golf ball coversinclude a first or inner layer or ply of a high acid (greater than 16weight percent acid) ionomer blend or, more preferably, a low acid (16weight percent acid or less) ionomer blend and second or outer layer orply comprised of a comparatively softer, low modulus ionomer, ionomerblend or other non-ionomeric thermoplastic or thermosetting elastomersuch as polyurethane or polyester elastomer. The multi-layer golf ballsof the present invention can be of standard or enlarged size.Preferably, the inner layer or ply includes a blend of low acid ionomersand has a Shore D hardness of 70 or greater and the outer cover layercomprised of polyurethane and has a Shore D hardness of about 45 (i.e.,Shore C hardness of about 65).

The present invention golf balls utilize a unique dual-coreconfiguration. Preferably, the cores comprise (i) an interior sphericalcenter component formed from a thermoset material, a thermoplasticmaterial, or combinations thereof; and (ii) a core layer disposed aboutthe spherical center component, the core layer formed from a thermosetmaterial, a thermoplastic material, or combinations thereof. The coresmay further comprise (iii) an optional outer core layer disposed aboutthe core layer. The outer core layer may be formed from a thermosetmaterial, a thermoplastic material, or combinations thereof.

Although the present invention is primarily directed to golf ballscomprising a dual core component and preferably in conjunction with amulti-layer cover as described herein, the present invention alsoincludes golf balls having a dual core component and conventional coverscomprising balata, various thermoplastic materials, cast polyurethanes,or any other known cover material.

It has been found that multi-layer golf balls having inner and outercover layers exhibit higher C.O.R. values and have greater traveldistance in comparison with balls made from a single cover layer. Inaddition, it has been found that use of an inner cover layer constructedof a blend of low acid (i.e., 16 weight percent acid or less) ionomerresins produces softer compression and higher spin rates than innercover layers constructed of high acid ionomer resins. This is compoundedby the fact that the softer polyurethane outer layer adds to thedesirable “feel” and high spin rate while maintaining respectableresilience. The soft outer layer allows the cover to deform more duringimpact and increases the area of contact between the club face and thecover, thereby imparting more spin on the ball. As a result, the softpolyurethane cover provides the ball with a balata-like feel andplayability characteristics with improved distance and durability.

Consequently, the overall combination of the unique dual coreconfiguration, described in greater detail herein, and the multi-layercover construction of inner and outer cover layers made, for example,from blends of low acid ionomer resins and polyurethane results in astandard size or oversized golf ball having enhanced resilience(improved travel distance) and durability (i.e. cut resistance, etc.)characteristics while maintaining and in many instances, improving theball's playability properties.

The combination of a low acid ionomer blend inner cover layer with asoft, relatively low modulus ionomer, polyurethane based elastomer outercover layer provides for good overall coefficient of restitution (i.e.,enhanced resilience) while at the same time demonstrating improvedcompression and spin. The outer cover layer generally contributes to amore desirable feel and spin, particularly at lower swing speeds withhighly lofted clubs such as half wedge shots.

Accordingly, the present invention is directed to a golf ball comprisinga dual-core configuration and an improved multi-layer cover whichproduces, upon molding each layer around a core to formulate amulti-layer cover, a golf ball exhibiting enhanced distance (i.e.,resilience) without adversely affecting, and in many instances,improving the ball's playability (hardness/softness) and/or durability(i.e., cut resistance, fatigue resistance, etc.) characteristics.

FIGS. 1 and 2 illustrate a preferred embodiment golf ball 5 inaccordance with the present invention. It will be understood that noneof the referenced figures are to scale. And so, the thicknesses andproportions of the various layers and the diameter of the various corecomponents are not necessarily as depicted. The golf ball 5 comprises amulti-layered cover 12 disposed about a core 10. The core 10 of the golfball can be formed of a solid, a liquid, or any other substances thatmay be utilized to form the novel dual core described herein. The core10 is preferably a dual core as described herein. The multi-layeredcover 12 comprises two layers: a first or inner layer or ply 14 and asecond or outer layer or ply 16. The inner layer 14 can be ionomer,ionomer blends, non-ionomer, non-ionomer blends, or blends of ionomerand non-ionomer. The outer layer 16 is softer than the inner layer andcan be ionomer, ionomer blends, non-ionomer, non-ionomer blends orblends of ionomer and non-ionomer.

In a first preferred embodiment, the inner layer 14 is comprised of ahigh acid (i.e., greater than 16 weight percent acid) ionomer resin orhigh acid ionomer blend. Preferably, the inner layer is comprised of ablend of two or more high acid (i.e., at least 16 weight percent acid)ionomer resins neutralized to various extents by different metalcations. The inner cover layer may or may not include a metal stearate(e.g., zinc stearate) or other metal fatty acid salt. The purpose of themetal stearate or other metal fatty acid salt is to lower the cost ofproduction without affecting the overall performance of the finishedgolf ball. In a second embodiment, the inner layer 14 is comprised of alow acid (i.e., 16 weight percent acid or less) ionomer blend.Preferably, the inner layer is comprised of a blend of two or more lowacid (i.e., 16 weight percent acid or less) ionomer resins neutralizedto various extents by different metal cations. The inner cover layer mayor may not include a metal stearate (e.g., zinc stearate) or other metalfatty acid salt. The purpose of the metal stearate or other metal fattyacid salt is to lower the cost of production without affecting theoverall performance of the finished golf ball.

Two principal properties involved in golf ball performance areresilience and hardness. Resilience is determined by the coefficient ofrestitution (C.O.R.), the constant “e” which is the ratio of therelative velocity of an elastic sphere after direct impact to thatbefore impact. As a result, the coefficient of restitution (“e”) canvary from 0 to 1, with 1 being equivalent to a perfectly or completelyelastic collision and 0 being equivalent to a perfectly or completelyinelastic collision.

Resilience (C.O.R.), along with additional factors such as club headspeed, angle of trajectory and ball configuration (i.e., dimple pattern)generally determine the distance a ball will travel when hit. Since clubhead speed and the angle of trajectory are factors not easilycontrollable by a manufacturer, factors of concern among manufacturersare the coefficient of restitution (C.O.R.) and the surfaceconfiguration of the ball.

The coefficient of restitution (C.O.R.) in solid core balls is afunction of the composition of the molded core and of the cover. Inballs containing a dual core (i.e., balls comprising an interiorspherical center component, a core layer disposed about the sphericalcenter component, and a cover), the coefficient of restitution is afunction of not only the composition of the cover, but also thecomposition and physical characteristics of the interior sphericalcenter component and the core layer. Both the dual core and the covercontribute to the coefficient of restitution in the golf balls of thepresent invention.

In this regard, the coefficient of restitution of a golf ball isgenerally measured by propelling a ball at a given speed against a hardsurface and measuring the ball's incoming and outgoing velocityelectronically. As mentioned above, the coefficient of restitution isthe ratio of the outgoing velocity to the incoming velocity. Thecoefficient of restitution must be carefully controlled in allcommercial golf balls in order for the ball to be within thespecifications regulated by the United States Golf Association(U.S.G.A.). Along this line, the U.S.G.A. standards indicate that a“regulation” ball cannot have an initial velocity (i.e., the speed ofthe club) exceeding 255 feet per second. Since the coefficient ofrestitution of a ball is related to the ball's initial velocity, it ishighly desirable to produce a ball having sufficiently high coefficientof restitution to closely approach the U.S.G.A. limit on initialvelocity, while having an ample degree of softness (i.e., hardness) toproduce enhanced playability (i.e., spin, etc.).

The hardness of the ball is the second principal property involved inthe performance of a golf ball. The hardness of the ball can affect theplayability of the ball on striking and the sound or “click” produced.Hardness is determined by the deformation (i.e., compression) of theball under various load conditions applied across the ball's diameter(i.e., the lower the compression value, the harder the material). Asindicated in U.S. Pat. No. 4,674,751, softer covers permit theaccomplished golfer to impart increased spin. This is because the softercovers deform on impact significantly more than balls having “harder”ionomeric resin covers. As a result, the better player is allowed toimpart fade, draw or backspin to the ball thereby enhancing playability.Such properties may be determined by various spin rate tests.

It has been found that a hard inner cover layer provides for asubstantial increase in resilience (i.e., enhanced distance) over knownmulti-layer covered balls. The softer outer cover layer provides fordesirable “feel” and high spin rate while maintaining respectableresiliency. The soft outer layer allows the cover to deform more duringimpact and increases the area of contact between the club face and thecover, thereby imparting more spin on the ball. As a result, the softcover provides the ball with a balata-like feel and playabilitycharacteristics with improved distance and durability. Consequently, theoverall combination of the inner and outer cover layers and the uniquedual core configuration results in a golf ball having enhancedresilience (improved travel distance) and durability (i.e., cutresistance, etc.) characteristics while maintaining and in manyinstances, improving the playability properties of the ball.

The combination of a dual core component and a hard inner cover layerwith a soft, relatively low modulus ionomer, ionomer blend or othernon-ionomeric thermoplastic elastomer outer cover layer provides forexcellent overall coefficient of restitution (i.e., excellentresilience) because of the improved resiliency produced by the innercover layer. Moreover, the configuration of, and the ability to selectthe materials used in, the dual core component enables the formulator toreadily tailor the end properties and characteristics of the resultinggolf ball. While some improvement in resiliency is also produced by theouter cover layer, the outer cover layer generally provides for a moredesirable feel and high spin, particularly at lower swing speeds withhighly lofted clubs such as half wedge shots.

Inner Cover Layer

The inner cover layer is harder than the outer cover layer and generallyhas a thickness in the range of 0.01 to 0.10 inches, preferably 0.03 to0.07 inches for a 1.68 inch ball and 0.05 to 0.10 inches for a 1.72 inch(or more) ball. The core and inner cover layer together form an innerball having a coefficient of restitution of 0.780 or more and morepreferably 0.790 or more, and a diameter in the range of 1.48-1.66inches for a 1.68 inch ball and 1.50-1.70 inches for a 1.72 inch (ormore) ball. The inner cover layer has a Shore D hardness of 60 or more.It is particularly advantageous if the golf balls of the invention havean inner layer with a Shore D hardness of 65 or more. Theabove-described characteristics of the inner cover layer provide aninner ball having a PGA compression of 100 or less. It is found thatwhen the inner ball has a PGA compression of 90 or less, excellentplayability results.

The inner layer compositions include the high acid ionomers such asthose developed by E.I. DuPont de Nemours & Company under the trademark“Surlyn®” and by Exxon Corporation under the trademark “Escor®” or tradename “Iotek”, or blends thereof. Examples of compositions which may beused as the inner layer herein are set forth in detail in a continuationof U.S. application Ser. No. 08/174,765, which is a continuation of U.S.application Ser. No. 07/776,803 filed Oct. 15, 1991, and Ser. No.08/493,089, which is a continuation of Ser. No. 07/981,751, which inturn is a continuation of Ser. No. 07/901,660 filed Jun. 19, 1992, allof which are incorporated herein by reference. Of course, the innerlayer high acid ionomer compositions are not limited in any way to thosecompositions set forth in said applications.

The high acid ionomers which may be suitable for use in formulating theinner layer compositions are ionic copolymers which are the metal, i.e.,sodium, zinc, magnesium, etc., salts of the reaction product of anolefin having from about 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from about 3 to 8 carbon atoms. Preferably,the ionomeric resins are copolymers of ethylene and either acrylic ormethacrylic acid. In some circumstances, an additional comonomer such asan acrylate ester (i.e., iso- or n-butylacrylate, etc.) can also beincluded to produce a softer terpolymer. The carboxylic acid groups ofthe copolymer are partially neutralized (i.e., approximately 10-100%,preferably 30-70%) by the metal ions. Each of the high acid ionomerresins which may be included in the inner layer cover compositions ofthe invention contains greater than about 16% by weight of a carboxylicacid, preferably from about 17% to about 25% by weight of a carboxylicacid, more preferably from about 18.5% to about 21.5% by weight of acarboxylic acid.

Although the inner layer cover composition of several embodiments of thepresent invention preferably includes a high acid ionomeric resin, thescope of the patent embraces all known high acid ionomeric resinsfalling within the parameters set forth above. Only a relatively limitednumber of these high acid ionomeric resins have recently becomecommercially available.

The high acid ionomeric resins available from Exxon under thedesignation “Escor®” and or “Iotek”, are somewhat similar to the highacid ionomeric resins available under the “Surlyn®” trademark. However,since the Escor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

Examples of the high acid methacrylic acid based ionomers found suitablefor use in accordance with this invention include Surlyn®8220 and 8240(both formerly known as forms of Surlyn AD-8422), Surlyn®9220 (zinccation), Surlyn®SEP-503-1 (zinc cation), and Surlyn®SEP-503-2 (magnesiumcation). According to DuPont, all of these ionomers contain from about18.5 to about 21.5% by weight methacrylic acid.

More particularly, Surlyn® AD-8422 is currently commercially availablefrom DuPont in a number of different grades (i.e., AD-8422-2, AD-8422-3,AD-8422-5, etc.) based upon differences in melt index. According toDuPont, Surlyn® 8422, which is believed recently to have beenredesignated as 8220 and 8240, offers the following general propertieswhen compared to Surlyn® 8920, the stiffest, hardest of all on the lowacid grades (referred to as “hard” ionomers in U.S. Pat. No. 4,884,814):

LOW ACID HIGH ACID (15 wt % Acid) (>20 wt % Acid) SURLYN ® SURLYN ®SURLYN ® 8920 8422-2 8422-3 IONOMER Cation Na Na Na Melt Index 1.2 2.81.0 Sodium, Wt % 2.3 1.9 2.4 Base Resin MI 60 60 60 MP¹, ° C. 88 86 85FP¹, ° C. 47 48.5 45 COMPRESSION MOLDING² Tensile Break, 4350 4190 5330psi Yield, psi 2880 3670 3590 Elongation, % 315 263 289 Flex Mod, 53.276.4 88.3 K psi Shore D 66 67 68 hardness ¹DSC second heat, 10° C./minheating rate. ²Samples compression molded at 150° C. annealed 24 hoursat 60° C. 8422-2, -3 were homogenized at 190° C. before molding.

In comparing Surlyn® 8920 to Surlyn® 8422-2 and Surlyn® 8422-3, it isnoted that the high acid Surlyn® 8422-2 and 8422-3 ionomers have ahigher tensile yield, lower elongation, slightly higher Shore D hardnessand much higher flexural modulus. Surlyn® 8920 contains 15 weightpercent methacrylic acid and is 59% neutralized with sodium.

In addition, Surlyn®SEP-503-1 (zinc cation) and Surlyn®SEP-503-2(magnesium cation) are high acid zinc and magnesium versions of theSurlyn®AD 8422 high acid ionomers. When compared to the Surlyn® AD 8422high acid ionomers, the Surlyn® SEP-503-1 and SEP-503-2 ionomers can bedefined as follows:

Surlyn ® Ionomer Ion Melt Index Neutralization % AD 8422-3 Na 1.0 45 SEP503-1 Zn 0.8 38 SEP 503-2 Mg 1.8 43

Further, Surlyn® 8162 is a zinc cation ionomer resin containingapproximately 20% by weight (i.e., 18.5-21.5% weight) methacrylic acidcopolymer that has been 30-70% neutralized. Surlyn® 8162 is currentlycommercially available from DuPont.

Examples of the high acid acrylic acid based ionomers suitable for usein the present invention also include the Escor® or Iotek high acidethylene acrylic acid ionomers produced by Exxon such as Ex 1001, 1002,959, 960, 989, 990, 1003, 1004, 993, 994. In this regard, Escor® orIotek 959 is a sodium ion neutralized ethylene-acrylic neutralizedethylene-acrylic acid copolymer. According to Exxon, Ioteks 959 and 960contain from about 19.0 to 21.0% by weight acrylic acid withapproximately 30 to about 70 percent of the acid groups neutralized withsodium and zinc ions, respectively. The physical properties of thesehigh acid acrylic acid based ionomers are set forth in Tables 1 and 2 asfollows:

TABLE 1 Physical Properties of Various Ionomers ESCOR ® ESCOR ® PROP-(IOTEK) (IOTEK) ERTY Ex1001 Ex1002 959 Ex1003 Ex1004 960 Melt 1.0 1.62.0 1.1 2.0 1.8 index, g/10 min Cation Na Na Na Zn Zn Zn Melting 183 183172 180 180.5 174 Point, ° F. Vicat 125 125 130 133 131 131 SofteningPoint, ° F. Tensile 34.4 22.5 4600 24.8 20.6 3500 @ Break MPa MPa psiMPa MPa psi Elongation 341 348 325 387 437 430 @ Break, % Hardness, 6362 66 54 53 57 Shore D Flexural 365 380 66,000 147 130 27,000 ModulusMPa MPa psi MPa MPa psi

TABLE 2 Physical Properties of Various Ionomers PROPERTY UNITS EX 989 EX993 EX 994 EX 990 Melt index g/10 min 1.30 1.25 1.32 1.24 Moisture ppm482 214 997 654 Cation type — Na Li K Zn M+ content by AAS wt % 2.740.87 4.54 0 Zn content by AAS wt % 0 0 0 3.16 Density kg/m³ 959 945 976977 Vicat softening point ° C. 52.5 51 50 55.0 Crystallization point °C. 40.1 39.8 44.9 54.4 Melting point ° C. 82.6 81.0 80.4 81.0 Tensile atyield MPa 23.8 24.6 22 16.5 Tensile at break MPa 32.3 31.1 29.7 23.8Elongation at break % 330 260 340 357 1% secant modulus MPa 389 379 312205 Flexural modulus MPa 340 368 303 183 Abrasion resistance mg 20.0 9.215.2 20.5 Hardness Shore D — 62 62.5 61 56 Zwick Rebound % 61 63 59 48

Furthermore, as a result of the development by the assignee of thisapplication of a number of new high acid ionomers neutralized to variousextents by several different types of metal cations, such as bymanganese, lithium, potassium, calcium and nickel cations, several newhigh acid ionomers and/or high acid ionomer blends besides sodium, zincand magnesium high acid ionomers or ionomer blends are now available forgolf ball cover production. It has been found that these new cationneutralized high acid ionomer blends produce inner cover layercompositions exhibiting enhanced hardness and resilience due tosynergies which occur during processing. Consequently, the metal cationneutralized high acid ionomer resins recently produced can be blended toproduce substantially higher C.O.R.'s than those produced by the lowacid ionomer inner cover compositions presently commercially available.

More particularly, several new metal cation neutralized high acidionomer resins have been produced by the inventors by neutralizing, tovarious extents, high acid copolymers of an alpha-olefin and an alpha,beta-unsaturated carboxylic acid with a wide variety of different metalcation salts. This discovery is the subject matter of U.S. applicationSer. No. 08/493,089, incorporated herein by reference. It has been foundthat numerous new metal cation neutralized high acid ionomer resins canbe obtained by reacting a high acid copolymer (i.e., a copolymercontaining greater than 16% by weight acid, preferably from about 17 toabout 25 weight percent acid, and more preferably about 20 weightpercent acid), with a metal cation salt capable of ionizing orneutralizing the copolymer to the extent desired (i.e., from about 10%to 90%).

The base copolymer is made up of greater than 16% by weight of an alpha,beta-unsaturated carboxylic acid and an alpha-olefin. Optionally, asoftening comonomer can be included in the copolymer. Generally, thealpha-olefin has from 2 to 10 carbon atoms and is preferably ethylene,and the unsaturated carboxylic acid is a carboxylic acid having fromabout 3 to 8 carbons. Examples of such acids include acrylic acid,methacrylic acid, ethacrylic acid, chloroacrylic acid, crotonic acid,maleic acid, fumaric acid, and itaconic acid, with acrylic acid beingpreferred.

The softening comonomer that can be optionally included in the innercover layer for the golf ball of the invention may be selected from thegroup consisting of vinyl esters of aliphatic carboxylic acids whereinthe acids have 2 to 10 carbon atoms, vinyl ethers wherein the alkylgroups contains 1 to 10 carbon atoms, and alkyl acrylates ormethacrylates wherein the alkyl group contains 1 to 10 carbon atoms.Suitable softening comonomers include vinyl acetate, methyl acrylate,methyl methacrylate, ethyl acrylate, ethyl methacrylate, butyl acrylate,butyl methacrylate, or the like.

Consequently, examples of a number of copolymers suitable for use toproduce the high acid ionomers included in the present inventioninclude, but are not limited to, high acid embodiments of anethylene/acrylic acid copolymer, an ethylene/methacrylic acid copolymer,an ethylene/itaconic acid copolymer, an ethylene/maleic acid copolymer,an ethylene/methacrylic acid/vinyl acetate copolymer, anethylene/acrylic acid/vinyl alcohol copolymer, etc. The base copolymerbroadly contains greater than 16% by weight unsaturated carboxylic acid,from about 39 to about 83% by weight ethylene and from 0 to about 40% byweight of a softening comonomer. Preferably, the copolymer containsabout 20% by weight unsaturated carboxylic acid and about 80% by weightethylene. Most preferably, the copolymer contains about 20% acrylic acidwith the remainder being ethylene.

Along these lines, examples of the preferred high acid base copolymerswhich fulfill the criteria set forth above, are a series ofethylene-acrylic copolymers which are commercially available from TheDow Chemical Company, Midland, Mich., under the “Primacor” designation.These high acid base copolymers exhibit the typical properties set forthbelow in Table 3.

TABLE 3 Typical Properties of Primacor Ethylene-Acrylic Acid CopolymersMELT TENSILE FLEXURAL VICAT PERCENT DENSITY, INDEX, YD. ST MODULUS SOFTPT SHORE D GRADE ACID glcc g/10 min (psi) (psi) (° C.) HARDNESS ASTMD-792 D-1238 D-638 D-790 D-1525 D-2240 5980 20.0 0.958  300.0 — 4800 4350 5990 20.0 0.955 1300.0 650 2600 40 42 5990 20.0 0.955 1300.0 650 320040 42 5981 20.0 0.960  300.0 900 3200 46 48 5981 20.0 0.960  300.0 9003200 46 48 5983 20.0 0.958  500.0 850 3100 44 45 5991 20.0 0.953 2600.0635 2600 38 40 ¹The Melt Index values are obtained according to ASTMD-1238, at 190° C.

Due to the high molecular weight of the Primacor 5981 grade of theethylene-acrylic acid copolymer, this copolymer is the more preferredgrade utilized in the invention.

The metal cation salts utilized in the invention are those salts whichprovide the metal cations capable of neutralizing, to various extents,the carboxylic acid groups of the high acid copolymer. These includeacetate, oxide or hydroxide salts of lithium, calcium, zinc, sodium,potassium, nickel, magnesium, and manganese.

Examples of such lithium ion sources are lithium hydroxide monohydrate,lithium hydroxide, lithium oxide and lithium acetate. Sources for thecalcium ion include calcium hydroxide, calcium acetate and calciumoxide. Suitable zinc ion sources are zinc acetate dihydrate and zincacetate, a blend of zinc oxide and acetic acid. Examples of sodium ionsources are sodium hydroxide and sodium acetate. Sources for thepotassium ion include potassium hydroxide and potassium acetate.Suitable nickel ion sources are nickel acetate, nickel oxide and nickelhydroxide. Sources of magnesium include magnesium oxide, magnesiumhydroxide, magnesium acetate. Sources of manganese include manganeseacetate and manganese oxide.

The new metal cation neutralized high acid ionomer resins are producedby reacting the high acid base copolymer with various amounts of themetal cation salts above the crystalline melting point of the copolymer,such as at a temperature from about 200° F. to about 500° F., preferablyfrom about 250° F. to about 350° F. under high shear conditions at apressure of from about 10 psi to 10,000 psi. Other well known blendingtechniques may also be used. The amount of metal cation salt utilized toproduce the new metal cation neutralized high acid based ionomer resinsis the quantity which provides a sufficient amount of the metal cationsto neutralize the desired percentage of the carboxylic acid groups inthe high acid copolymer. The extent of neutralization is generally fromabout 10% to about 90%.

As indicated below in Table 4 and more specifically in Example 1 in U.S.application Ser. No. 08/493,089, a number of new types of metal cationneutralized high acid ionomers can be obtained from the above indicatedprocess. These include new high acid ionomer resins neutralized tovarious extents with manganese, lithium, potassium, calcium and nickelcations. In addition, when a high acid ethylene/acrylic acid copolymeris utilized as the base copolymer component of the invention and thiscomponent is subsequently neutralized to various extents with the metalcation salts producing acrylic acid based high acid ionomer resinsneutralized with cations such as sodium, potassium, lithium, zinc,magnesium, manganese, calcium and nickel, several new cation neutralizedacrylic acid based high acid ionomer resins are produced.

TABLE 4 Metal Cation Neutralized High Acid Ionomers Formulation Wt-%Wt-% Melt Shore D No. Cation Salt Neutralization Index C.O.R. Hardness 1(NaOH) 6.98 67.5 0.9 .804 71  2(NaOH) 5.66 54.0 2.4 .808 73  3(NaOH)3.84 35.9 12.2 .812 69  4(NaOH) 2.91 27.0 17.5 .812 (brittte)  5(MnAc)19.6 71.7 7.5 .809 73  6(MnAc) 23.1 88.3 3.5 .814 77  7(MnAc) 15.3 53.07.5 .810 72  8(MnAc) 26.5 106 0.7 .813 (brittle)  9(LiOH) 4.54 71.3 0.6.810 74 10(LiOH) 3.38 52.5 4.2 .818 72 11(LiOH) 2.34 35.9 18.6 .815 7212(KOH) 5.30 36.0 19.3 Broke 70 13(KOH) 8.26 57.9 7.18 .804 70 14(KOH)10.7 77.0 4.3 .801 67 15(ZnAc) 17.9 71.5 0.2 .806 71 16(ZnAc) 13.9 53.00.9 .797 69 17(ZnAc) 9.91 36.1 3.4 .793 67 18(MgAc) 17.4 70.7 2.8 .81474 19(MgAc) 20.6 87.1 1.5 .815 76 20(MgAc) 13.8 53.8 4.1 .814 7421(CaAc) 13.2 69.2 1.1 .813 74 22(CaAc) 7.12 34.9 10.1 .808 70 23(MgO)2.91 53.5 2.5 .813 24(MgO) 3.85 71.5 2.8 .808 25(MgO) 4.76 89.3 1.1 .80926(MgO) 1.96 35.7 7.5 .815 27(NiAc) 13.04 61.1 0.2 .802 71 28(NiAc)10.71 48.9 0.5 .799 72 29(NiAc) 8.26 36.7 1.8 .796 69 30(NiAc) 5.66 24.47.5 .786 64 Controls: 50/50 Blend of Ioteks 8000/7030 C.O.R. = .810/65Shore D Hardness DuPont High Acid Surlyn ® 8422 (Na) C.O.R. = .811/70Shore D Hardness DuPont High Acid Surlyn ® 8162 (Zn) C.O.R. = .807/65Shore D Hardness Exxon High Acid Iotek EX-960 (Zn) C.O.R. = .796/65Shore D Hardness Control for Formulations 23-26 is 50/50 Iotek8000/7030, C.O.R. = .814, Formulation 26 C.O.R. was normalized to thatcontrol accordingly Control for Formulation Nos. 27-30 is 50/50 Iotek8000/7030, C.O.R. = .807

When compared to low acid versions of similar cation neutralized ionomerresins, the new metal cation neutralized high acid ionomer resinsexhibit enhanced hardness, modulus and resilience characteristics. Theseare properties that are particularly desirable in a number ofthermoplastic fields, including the field of golf ball manufacturing.

When utilized in the construction of the inner layer of a multi-layeredgolf ball, it has been found that the new acrylic acid based high acidionomers extend the range of hardness beyond that previously obtainablewhile maintaining the beneficial properties (i.e. durability, click,feel, etc.) of the softer low acid ionomer covered balls, such as ballsproduced utilizing the low acid ionomers disclosed in U.S. Pat. Nos.4,884,814 and 4,911,451.

Moreover, as a result of the development of a number of new acrylic acidbased high acid ionomer resins neutralized to various extents by severaldifferent types of metal cations, such as manganese, lithium, potassium,calcium and nickel cations, several new ionomers or ionomer blends arenow available for production of an inner cover layer of a multi-layeredgolf ball. By using these high acid ionomer resins, harder, stifferinner cover layers having higher C.O.R.s, and thus longer distance, canbe obtained.

More preferably, it has been found that when two or more of theabove-indicated high acid ionomers, particularly blends of sodium andzinc high acid ionomers, are processed to produce the covers ofmulti-layered golf balls, (i.e., the inner cover layer herein) theresulting golf balls will travel further than previously knownmulti-layered golf balls produced with low acid ionomer resin covers dueto the balls' enhanced coefficient of restitution values.

The low acid ionomers which may be suitable for use in formulating theinner layer compositions of several of the embodiments of the subjectinvention are ionic copolymers which are the metal, i.e., sodium, zinc,magnesium, etc., salts of the reaction product of an olefin having fromabout 2 to 8 carbon atoms and an unsaturated monocarboxylic acid havingfrom about 3 to 8 carbon atoms. Preferably, the ionomeric resins arecopolymers of ethylene and either acrylic or methacrylic acid. In somecircumstances, an additional comonomer such as an acrylate ester (i.e.,iso- or n-butylacrylate, etc.) can also be included to produce a softerterpolymer. The carboxylic acid groups of the copolymer are partiallyneutralized (i.e., approximately 10-100%, preferably 30-70%) by themetal ions. Each of the low acid ionomer resins which may be included inthe inner layer cover compositions of the invention contains 16% byweight of less of a carboxylic acid.

The inner layer compositions include the low acid ionomers such as thosedeveloped and sold by E. I. DuPont de Nemours & Company under thetrademark “Surlyn®” and by Exxon Corporation under the trademark“Escor®” or tradename “Iotek,” or blends thereof.

The low acid ionomer resins available from Exxon under the designation“Escor®” and/or “Iotek,” are somewhat similar to the low acid ionomericresins available under the “Surlyn®” trademark. However, since theEscor®/Iotek ionomeric resins are sodium or zinc salts ofpoly(ethylene-acrylic acid) and the “Surlyn®” resins are zinc, sodium,magnesium, etc. salts of poly(ethylene-methacrylic acid), distinctdifferences in properties exist.

When utilized in the construction of the inner layer of a multi-layeredgolf ball, it has been found that the low acid ionomer blends extend therange of compression and spin rates beyond that previously obtainable.More preferably, it has been found that when two or more low acidionomers, particularly blends of sodium and zinc ionomers, are processedto produce the covers of multi-layered golf balls, (i.e., the innercover layer herein) the resulting golf balls will travel further and atan enhanced spin rate than previously known multi-layered golf balls.Such an improvement is particularly noticeable in enlarged or oversizedgolf balls.

The use of an inner layer formulated from blends of lower acid ionomersproduces multi-layer golf balls having enhanced compression and spinrates. These are the properties desired by the more skilled golfer.

In yet another embodiment of the inner cover layer, a blend of high andlow acid ionomer resins is used. These can be the ionomer resinsdescribed above, combined in a weight ratio which preferably is withinthe range of 10:90 to 90:10 parts of high and low acid ionomer resins.

A further additional embodiment of the inner cover layer is primarilybased upon the use of a fully non-ionomeric thermoplastic material.Suitable non-ionomeric materials include metallocene catalyzedpolyolefins or polyamides, polyamide/ionomer blends, polyphenyleneether/ionomer blends, etc., which have a shore D hardness of ≧60 and aflex modulus of greater than about 30,000 psi, or other hardness andflex modulus values which are comparable to the properties of theionomers described above. Other suitable materials include, but are notlimited to, thermoplastic or thermosetting polyurethanes, a polyesterelastomer such as that marketed by DuPont under the trademark Hytrel®,or a polyester amide such as that marketed by Elf Atochem S. A. underthe trademark Pebax®, a blend of two or more non-ionomeric thermoplasticelastomers, or a blend of one or more ionomers and one or morenon-ionomeric thermoplastic elastomers. These materials can be blendedwith the ionomers described above in order to reduce cost relative tothe use of higher quantities of ionomer.

Outer Cover Layer

While the dual core component described below, and the hard inner coverlayer formed thereon, provide the multi-layer golf ball with power anddistance, the outer cover layer 16 is comparatively softer than theinner cover layer. The softness provides for the feel and playabilitycharacteristics typically associated with balata or balata-blend balls.The outer cover layer or ply is comprised of a relatively soft, lowmodulus (about 1,000 psi to about 10,100 psi) and, in an alternateembodiment, low acid (less than 16 weight percent acid) ionomer, anionomer blend, a non-ionomeric thermoplastic or thermosetting materialsuch as, but not limited to, a metallocene catalyzed polyolefin such asEXACT material available from EXXON, a polyurethane, a polyesterelastomer such as that marketed by DuPont under the trademark Hytrel®,or a polyester amide such as that marketed by Elf Atochem S. A. underthe trademark Pebax®, a blend of two or more non-ionomeric thermoplasticor thermosetting materials, or a blend of one or more ionomers and oneor more non-ionomeric thermoplastic materials. The outer layer is fairlythin (i.e. from about 0.010 to about 0.10 inches in thickness, moredesirably 0.03 to 0.06 inches in thickness for a 1.680 inch ball and0.04 to 0.07 inches in thickness for a 1.72 inch or more ball), butthick enough to achieve desired playability characteristics whileminimizing expense. Thickness is defined as the average thickness of thenon-dimpled areas of the outer cover layer. The outer cover layer, suchas layer 16, 16 has a Shore D hardness of 55 or less, and morepreferably 50 or less.

In one embodiment, the outer cover layer preferably is formed from anionomer which constitutes at least 75 weight % of an acrylateester-containing ionic copolymer or blend of acrylate ester-containingionic copolymers. This type of outer cover layer in combination with thecore and inner cover layer described above results in golf ball covershaving a favorable combination of durability and spin rate. The one ormore acrylate ester-containing ionic copolymers each contain an olefin,an acrylate ester, and an acid. In a blend of two or more acrylateester-containing ionic copolymers, each copolymer may contain the sameor a different olefin, acrylate ester and acid than are contained in theother copolymers. Preferably, the acrylate ester-containing ioniccopolymer or copolymers are terpolymers, but additional monomers can becombined into the copolymers if the monomers do not substantially reducethe scuff resistance or other good playability properties of the cover.

For a given copolymer, the olefin is selected from the group consistingof olefins having 2 to 8 carbon atoms, including, as non-limitingexamples, ethylene, propylene, butene-1, hexene-1 and the like.Preferably the olefin is ethylene.

The acrylate ester is an unsaturated monomer having from 1 to 21 carbonatoms which serves as a softening comonomer. The acrylate esterpreferably is methyl, ethyl, n-propyl, n-butyl, n-octyl, 2-ethylhexyl,or 2-methoxyethyl 1-acrylate, and most preferably is methyl acrylate orn-butyl acrylate. Another suitable type of softening comonomer is analkyl vinyl ether selected from the group consisting of n-butyl,n-hexyl, 2-ethylhexyl, and 2-methoxyethyl vinyl ethers.

The acid is a mono- or dicarboxylic acid and preferably is selected fromthe group consisting of methacrylic, acrylic, ethacrylic,a-chloroacrylic, crotonic, maleic, fumaric, and itaconic acid, or thelike, and half esters of maleic, fumaric and itaconic acid, or the like.The acid group of the copolymer is 10-100% neutralized with any suitablecation, for example, zinc, sodium, magnesium, lithium, potassium,calcium, manganese, nickel, chromium, tin, aluminum, or the like. It hasbeen found that particularly good results are obtained when theneutralization level is about 50-100%.

The one or more acrylate ester-containing ionic copolymers each has anindividual Shore D hardness of about 5-64. The overall Shore D hardnessof the outer cover is 55 or less, and generally is 40-55. It ispreferred that the overall Shore D hardness of the outer cover is in therange of 40-50 in order to impart particularly good playabilitycharacteristics to the ball.

The outer cover layer of the invention is formed over a core to resultin a golf ball having a coefficient of restitution of at least 0.770,more preferably at least 0.780, and most preferably at least 0.790. Thecoefficient of restitution of the ball will depend upon the propertiesof both the core and the cover. The PGA compression of the golf ball is100 or less, and preferably is 90 or less.

The acrylate ester-containing ionic copolymer or copolymers used in theouter cover layer can be obtained by neutralizing commercially availableacrylate ester-containing acid copolymers such as polyethylene-methylacrylate-acrylic acid terpolymers, including ESCOR ATX (Exxon ChemicalCompany) or poly (ethylene-butyl acrylate-methacrylic acid) terpolymers,including NUCREL (DuPont Chemical Company). Particularly preferredcommercially available materials include ATX 320, ATX 325, ATX 310, ATX350, and blends of these materials with NUCREL 010 and NUCREL 035. Theacid groups of these materials and blends are neutralized with one ormore of various cation salts including zinc, sodium, magnesium, lithium,potassium, calcium, manganese, nickel, etc. The degree of neutralizationranges from 10-100%. Generally, a higher degree of neutralizationresults in a harder and tougher cover material. The properties ofnon-limiting examples of commercially available un-neutralized acidterpolymers which can be used to form the golf ball outer cover layersof the invention are provided below in Table 5.

TABLE 5 Properties of Un-Neutralized Acid Terpolymers Flex Melt IndexModulus dg/min Acid No. MPa Hardness Trade Name ASTM D 1238 % KOH/g(ASTM D790) (Shore D) ATX 310 6 45 80 44 ATX 320 5 45 50 34 ATX 325 2045 9 30 ATX 350 6 15 20 28 Nucrel 010 11 60 40 40 Nucrel 035 35 60 59 40

The ionomer resins used to form the outer cover layers can be producedby reacting the acrylate ester-containing acid copolymer with variousamounts of the metal cation salts at a temperature above the crystallinemelting point of the copolymer, such as a temperature from about 200° F.to about 500° F., preferably from about 250° F. to about 350° F., underhigh shear conditions at a pressure of from about 100 psi to 10,000 psi.Other well known blending techniques may also be used. The amount ofmetal cation salt utilized to produce the neutralized ionic copolymersis the quantity which provides a sufficient amount of the metal cationsto neutralize the desired percentage of the carboxylic acid groups inthe high acid copolymer. When two or more different copolymers are to beused, the copolymers can be blended before or after neutralization.Generally, it is preferable to blend the copolymers before they areneutralized to provide for optimal mixing.

The compatibility of the acrylate ester-containing copolymers with eachother in a copolymer blend produces a golf ball outer cover layer havinga surprisingly good scuff resistance for a given hardness of the outercover layer. The golf ball according to the invention has a scuffresistance of no higher than 3.0. It is preferred that the golf ball hasa scuff resistance of no higher than about 2.5 to ensure that the golfball is scuff resistant when used in conjunction with a variety of typesof clubs, including sharp-grooved irons, which are particularly inclinedto result in scuffing of golf ball covers. The best results according tothe invention are obtained when the outer cover layer has a scuffresistance of no more than about 2.0.

Additional materials may also be added to the inner and outer coverlayer of the present invention as long as they do not substantiallyreduce the playability properties of the ball. Such materials includedyes (for example, Ultramarine Blue sold by Whitaker, Clark, and Danielsof South Plainsfield, N.J.) (see U.S. Pat. No. 4,679,795), pigments suchas titanium dioxide, zinc oxide, barium sulfate and zinc sulfate; UVabsorbers; antioxidants; antistatic agents; optical brighteners; andstabilizers. Moreover, the cover compositions of the present inventionmay also contain softening agents such as those disclosed in U.S. Pat.Nos. 5,312,857 and 5,306,760, including plasticizers, metal stearates,processing acids, etc., and reinforcing materials such as glass fibersand inorganic fillers, as long as the desired properties produced by thegolf ball covers of the invention are not impaired.

The outer layer in another embodiment of the invention includes a blendof a soft (low acid) ionomer resin with a small amount of a hard (highacid) ionomer resin. A low modulus ionomer suitable for use in the outerlayer blend has a flexural modulus measuring from about 1,000 to about10,000 psi, with a hardness of about 20 to about 40 on the Shore Dscale. A high modulus ionomer herein is one which measures from about15,000 to about 70,000 psi as measured in accordance with ASTM methodD-790. The hardness may be defined as at least 50 on the Shore D scaleas measured in accordance with ASTM method D-2240.

Soft ionomers primarily are used in formulating the hard/soft blends ofthe cover compositions. These ionomers include acrylic acid andmethacrylic acid based soft ionomers. They are generally characterizedas comprising sodium, zinc, or other mono- or divalent metal cationsalts of a terpolymer of an olefin having from about 2 to 8 carbonatoms, methacrylic acid, acrylic acid, or another, α, β-unsaturatedcarboxylic acid, and an unsaturated monomer of the acrylate ester classhaving from 1 to 21 carbon atoms. The soft ionomer is preferably madefrom an acrylic acid base polymer is an unsaturated monomer of theacrylate ester class.

Certain ethylene-acrylic acid based soft ionomer resins developed by theExxon Corporation under the designation “Iotek 7520” (referred toexperimentally by differences in neutralization and melt indexes as LDX195, LDX 196, LDX 218 and LDX 219) may be combined with known hardionomers such as those indicated above to produce the inner and outercover layers. The combination produces higher C.O.R.s at equal or softerhardness, higher melt flow (which corresponds to improved, moreefficient molding, i.e., fewer rejects] as well as significant costsavings versus the outer layer of multi-layer balls produced by otherknown hard-soft ionomer blends as a result of the lower overall rawmaterials cost and improved yields.

While the exact chemical composition of the resins to be sold by Exxonunder the designation Iotek 7520 is considered by Exxon to beconfidential and proprietary information, Exxon's experimental productdata sheet lists the following physical properties of the ethyleneacrylic acid zinc ionomer developed by Exxon:

TABLE 6 Physical Properties of Iotek 7520 ASTM Method Units TypicalProperty Value Melt Index D-1238 g/10 min. 2 Density D-1505 kg/m³ 0.962Cation Zinc Melting Point D-3417 ° C. 66 Crystallization D-3417 ° C. 49Point Vicat Softening D-1525 ° C. 42 Point Plaque Properties (2 mm thickCompression Molded Plaques) Tensile at Break D-638  MPa 10 Yield PointD-638  MPa None Elongation at Break D-638  % 760 1% Secant ModulusD-638  MPa 22 Shore D Hardness D-2240 32 Flexural Modulus D-790  MPa 26Zwick Rebound ISO 4862 % 52 De Mattia Flex D-430  Cycles >5000Resistance

In addition, test data collected by the inventors indicates that Iotek7520 resins have Shore D hardnesses of about 32 to 36 (per ASTM D-2240),melt flow indexes of 3±0.5 g/10 min (at 190° C. per ASTM D-1288), and aflexural modulus of about 2500-3500 psi (per ASTM D-790). Furthermore,testing by an independent testing laboratory by pyrolysis massspectrometry indicates that Iotek 7520 resins are generally zinc saltsof a terpolymer of ethylene, acrylic acid, and methyl acrylate.

Furthermore, the inventors have found that a newly developed grade of anacrylic acid based soft ionomer available from the Exxon Corporationunder the designation Iotek 7510 is also effective when combined withthe hard ionomers indicated above in producing golf ball coversexhibiting higher C.O.R. values at equal or softer hardness than thoseproduced by known hard-soft ionomer blends. In this regard, Iotek 7510has the advantages (i.e. improved flow, higher C.O.R. values at equalhardness, increased clarity, etc.) produced by the Iotek 7520 resin whencompared to the methacrylic acid base soft ionomers known in the art(such as the Surlyn® 8625 and Surlyn® 8629 combinations disclosed inU.S. Pat. No. 4,8884,814).

In addition, Iotek 7510, when compared to Iotek 7520, produces slightlyhigher C.O.R. values at equal softness/hardness due to the Iotek 7510'shigher hardness and neutralization. Similarly, Iotek 7510 producesbetter release properties (from the mold cavities) due to its slightlyhigher stiffness and lower flow rate than Iotek 7520. This is importantin production where the soft covered balls tend to have lower yieldscaused by sticking in the molds and subsequent punched pin marks fromthe knockouts.

According to Exxon, Iotek 7510 is of similar chemical composition asIotek 7520 (i.e. a zinc salt of a terpolymer of ethylene, acrylic acid,and methyl acrylate) but is more highly neutralized. Based upon FTIRanalysis, Iotek 7520 is estimated to be about 30-40 wt. % neutralizedand Iotek 7510 is estimated to be about 40-60 wt. % neutralized. Thetypical properties of Iotek 7510 in comparison of those of Iotek 7520 incomparison of those of Iotek 7520 are set forth below:

TABLE 7 Physical Properties of Iotek 7510 in Comparison to Iotek 7520IOTEK 7520 IOTEK 7510 MI, g/10 min 2.0 0.8 Density, g/cc 0.96 0.97Melting Point, ° F. 151 149 Vicat Softening Point, ° F. 108 109 FlexModulus, psi 3800 5300 Tensile Strength, psi 1450 1750 Elongation, % 760690 Hardness, Shore D 32 35

The hard ionomer resins utilized to produce the outer cover layercomposition hard/soft blends include ionic copolymers which are thesodium, zinc, magnesium, lithium, etc. salts of the reaction product ofan olefin having from 2 to 8 carbon atoms and an unsaturatedmonocarboxylic acid having from 3 to 8 carbon atoms. The carboxylic acidgroups of the copolymer may be totally or partially (i.e. approximately15-75 percent) neutralized.

The hard ionomeric resins are likely copolymers of ethylene and acrylicand/or methacrylic acid, with copolymers of ethylene and acrylic acidbeing the most preferred. Two or more types of hard ionomeric resins maybe blended into the outer cover layer compositions in order to producethe desired properties of the resulting golf balls.

As discussed earlier herein, the hard ionomeric resins introduced underthe designation Escor® and sold under the designation “Iotek” aresomewhat similar to the hard ionomeric resins sold under the Surlyn®trademark. However, since the “Iotek” ionomeric resins are sodium orzinc salts of poly(ethylene-acrylic acid) and the Surlyn® resins arezinc or sodium salts of poly(ethylene-methacrylic acid) some distinctdifferences in properties exist. As more specifically indicated in thedata set forth below, the hard “Iotek” resins (i.e., the acrylic acidbased hard ionomer resins) are the more preferred hard resins for use informulating the outer layer blends for use in the present invention. Inaddition, various blends of “Iotek” and Surlyn® hard ionomeric resins,as well as other available ionomeric resins, may be utilized in thepresent invention in a similar manner.

Examples of commercially available hard ionomeric resins which may beused in the present invention in formulating the outer cover blendsinclude the hard sodium ionic copolymer sold under the trademark Surlyn®8940 and the hard zinc ionic copolymer sold under the trademark Surlyn®9910. Surlyn® 8940 is a copolymer of ethylene with methacrylic acid andabout 15 weight percent acid which is about 29 percent neutralized withsodium ions. This resin has an average melt flow index of about 2.8.Surlyn® 9910 is a copolymer of ethylene and methacrylic acid with about15 weight percent acid which is about 58 percent neutralized with zincions. The average melt flow index of Surlyn® 9910 is about 0.7. Thetypical properties of Surlyn® 9910 and 8940 are set forth below in Table8:

TABLE 8 Typical Properties of Commercially Available Hard Surlyn ®Resins Suitable for Use in the Outer Layer Blends of the PresentInvention ASTM D 8940 9910 8920 8528 9970 9730 Cation Type Sodium ZincSodium Sodium Zinc Zinc Melt flow index, D-1238 2.8 0.7 0.9 1.3 14.0 1.6gms/10 min. Specific Gravity, D-792 0.95 0.97 0.95 0.94 0.95 0.95 g/cm³Hardness, Shore D D-2240 66 64 66 60 62 63 Tensile Strength, D-638 (4.8)(3.6) (5.4) (4.2) (3.2) (4.1) (kpsi), MPa 33.1 24.8 37.2 29.0 22.0 28.0Elongation, % D-638 470 290 350 450 460 460 Flexural Modulus, D-790 (51)(48) (55) (32) (28) (30) (kpsi) MPa 350 330 380 220 190 210 TensileImpact (23° C.) KJ/m² (ft.-lbs./in²) D-1822S 1020 1020 865 1160 760 1240(485) (485) (410) (550) (360) (590) Vicat Temperature, ° C. D-1525 63 6258 73 61 73

Examples of the more pertinent acrylic acid based hard ionomer resinsuitable for use in the present outer cover composition sold under the“Iotek” trade name by the Exxon Corporation include Iotek 8000, 8010,8020, 8030, 7030, 7010, 7020, 1002, 1003, 959 and 960. The physicalproperties of Iotek 959 and 960 are shown above. The typical propertiesof the remainder of these and other Iotek hard ionomers suited for usein formulating the outer layer cover composition are set forth below inTable 9:

TABLE 9 Typical Properties of Iotek Ionomers ASTM Method Units 4000 40108000 8020 8030 Resin Properties Cation type zinc zinc sodium sodiumsodium Melt index D-1238 g/10 min. 2.5 1.5 0.8 1.6 2.8 Density D-1505kg/m³ 963 963 954 960 960 Melting Point D-3417 ° C. 90 90 90 87.5 87.5Crystallization Point D-3417 ° C. 62 64 56 53 55 Vicat Softening PointD-1525 ° C. 62 63 61 64 67 % Weight Acrylic Acid 16 11 % of Acid Groups30 40 cation neutralized Plaque Properties (3 mm thick, compressionmolded) Tensile at break D-638 MPa 24 26 36 31.5 28 Yield point D-638MPa none none 21 21 23 Elongation at break D-638 % 395 420 350 410 3951% Secant modulus D-638 MPa 160 160 300 350 390 Shore Hardness D D-2240— 55 55 61 58 59 Film Properties (50 micron film 2.2:1 Blow-up ratio)Tensile at Break MD D-882 MPa 41 39 42 52 47.4 TD D-882 MPa 37 38 38 3840.5 Yield point MD D-882 MPa 15 17 17 23 21.6 TD D-882 MPa 14 15 15 2120.7 Elongation at Break MD D-882 % 310 270 260 295 305 TD D-882 % 360340 280 340 345 1% Secant modulus MD D-882 MPa 210 215 390 380 380 TDD-882 MPa 200 225 380 350 345 Dart Drop Impact D-1709 g/micron 12.4 12.520.3 ASTM Method Units 7010 7020 7030 Resin Properties Cation type zinczinc zinc Melt Index D-1238 g/10 min. 0.8 1.5 2.5 Density D-1505 kg/m³960 960 960 Melting Point D-3417 ° C. 90 90 90 Crystallization PointD-3417 ° C. — — — Vicat Softening Point D-1525 ° C. 60 63 62.5 % WeightAcrylic Acid — — — % of Acid Groups Cation — — — Neutralized PlaqueProperties (3 mm thick, compression molded) Tensile at break D-638 MPa38 38 38 Yield Point D-638 MPa none none none Elongation at break D-638% 500 420 395 1% Secant modulus D-638 MPa — — — Shore Hardness D  D-2240— 57 55 55

It has been determined that when hard/soft ionomer blends are used forthe outer cover layer, good results are achieved when the relativecombination is in a range of about 3-25 percent hard ionomer and about75-97 percent soft ionomer.

Moreover, in alternative embodiments, the outer cover layer formulationmay also comprise up to 100 wt % of a soft, low modulus non-ionomericthermoplastic material including a polyester polyurethane such as B. F.Goodrich Company's Estane® polyester polyurethane X-4517. Thenon-ionomeric thermoplastic material may be blended with a soft ionomer.For example, polyamides blend well with soft ionomer. According to B.F.Goodrich, Estane® X-4517 has the following properties:

Properties of Estane ® X-4517 Tensile 1430 100% 815 200% 1024 300% 1193Elongation 641 Youngs Modulus 1826 Hardness A/D 88/39 Bayshore Rebound59 Solubility in Water Insoluble Melt processing temperature >350° F.(>177° C.) Specific Gravity (H₂O = 1) 1.1-1.3

Other soft, relatively low modulus non-ionomeric thermoplasticelastomers may also be utilized to produce the outer cover layer as longas the non-ionomeric thermoplastic elastomers produce the playabilityand durability characteristics desired without adversely effecting theenhanced travel distance characteristic produced by the high acidionomer resin composition. These include, but are not limited tothermoplastic polyurethanes such as Texin thermoplastic polyurethanesfrom Mobay Chemical Co. and the Pellethane thermoplastic polyurethanesfrom Dow Chemical Co.; non-ionomeric thermoset polyurethanes includingbut not limited to those disclosed in U.S. Pat. No. 5,334,673;cross-linked metallocene catalyzed polyolefins; ionomer/rubber blendssuch as those in Spalding U.S. Pat. Nos. 4,986,545; 5,098,105 and5,187,013; and, Hytrel polyester elastomers from DuPont and Pebaxpolyesteramides from Elf Atochem S. A.

Dual Core

As noted, the present invention golf balls utilize a unique dual coreconfiguration. Preferably, the cores comprise (i) an interior sphericalcenter component formed from a thermoset material, a thermoplasticmaterial, or combinations thereof and (ii) a core layer disposed aboutthe spherical center component, the core layer formed from a thermosetmaterial, a thermoplastic material, or combinations thereof. Mostpreferably, the core layer is disposed immediately adjacent to, and inintimate contact with the center component. The cores may furthercomprise (iii) an optional outer core layer disposed about the corelayer. Most preferably, the outer core layer is disposed immediatelyadjacent to, and in intimate contact with the core layer. The outer corelayer may be formed from a thermoset material, a thermoplastic material,or combinations thereof.

The present invention provides several additionally preferred embodimentgolf balls utilizing the unique dual core configuration and thepreviously described cover layers. Referring to FIG. 3, a preferredembodiment golf ball 35 is illustrated comprising a core 30 formed froma thermoset material surrounded by a core layer 32 formed from athermoplastic material. A multi-layer cover 34 surrounds the core 30 andthe core layer 32. The multi-layer cover 34 preferably corresponds tothe previously described multi-layer cover 12.

As illustrated in FIG. 4, another preferred embodiment golf ball 45 inaccordance with the present invention is depicted. The preferredembodiment golf ball 45 comprises a core 40 formed from a thermoplasticmaterial surrounded by a core layer 42. The core layer 42 is formed froma thermoset material. A multi-layer cover 44 surrounds the core 40 andthe core layer 42. Again, the multi-layer cover 44 preferablycorresponds to the previously described multi-layer cover 12.

FIG. 5 illustrates yet another preferred embodiment golf ball 55 inaccordance with the present invention. The preferred embodiment golfball 55 comprises a core 50 formed from a thermoplastic material. A corelayer 52 surrounds the core 50. The core layer 52 is formed from athermoplastic material which may be the same as the material utilizedfor the core 50, or one or more other or different thermoplasticmaterials. The preferred embodiment golf ball 55 utilizes an optionalouter core layer 54 that surrounds the core component 50 and the corelayer 52. The outer core layer 54 is formed from a thermoplasticmaterial which may be the same or different than any of thethermoplastic materials utilized for the core 50 and the core layer 52.The golf ball 55 further comprises a multi-layer cover 56 that ispreferably similar to the previously described multi-layer cover 12.

FIG. 6 illustrates yet another preferred embodiment golf ball 65 inaccordance with the present invention. The preferred embodiment golfball 65 comprises a core 60 formed from a thermoplastic, thermosetmaterial, or any combination of a thermoset and thermoplastic material.A core layer 62 surrounds the core 60. The core layer 62 is formed froma thermoset material. The preferred embodiment golf ball 65 alsocomprises an optional outer core layer 64 formed from a thermoplasticmaterial. A multi-layer cover 66, preferably similar to the previouslydescribed multi-layer cover 12, is disposed about, and generallysurrounds, the core 60, the core layer 62 and the outer core 64.

A wide array of thermoset materials can be utilized in the presentinvention dual cores. Examples of suitable thermoset materials includebutadiene or any natural or synthetic elastomer, including metallocenepolyolefins, polyurethanes, silicones, polyamides, polyureas, orvirtually any irreversibly cross-linked resin system. It is alsocontemplated that epoxy, phenolic, and an array of unsaturated polyesterresins could be utilized.

The thermoplastic material utilized in the present invention golf ballsand, particularly their dual cores, may be nearly any thermoplasticmaterial. Examples of typical thermoplastic materials for incorporationin the golf balls of the present invention include, but are not limitedto, ionomers, polyurethane thermoplastic elastomers, and combinationsthereof. It is also contemplated that a wide array of otherthermoplastic materials could be utilized, such as polysulfones,fluoropolymers, polyamide-imides, polyarylates, polyaryletherketones,polyaryl sulfones/polyether sulfones, polybenzimidazoles,polyether-imides, polyimides, liquid crystal polymers, polyphenylenesulfides; and specialty high-performance resins, which would includefluoropolymers, polybenzimidazole, and ultrahigh molecular weightpolyethylenes.

Additional examples of suitable thermoplastics include metallocenes,polyvinyl chlorides, acrylonitrile-butadiene-styrenes, acrylics,styrene-acrylonitriles, styrene-maleic anhydrides, polyamides (nylons),polycarbonates, polybutylene terephthalates, polyethyleneterephthalates, polyphenylene ethers/polyphenylene oxides, reinforcedpolypropylenes, and high-impact polystyrenes.

Preferably, the thermoplastic materials have relatively high meltingpoints, such as a melting point of at least about 300° F. Severalexamples of these preferred thermoplastic materials and which arecommercially available include, but are not limited to, Capron (a blendof nylon and ionomer), Lexan polycarbonate, Pebax, and Hytrel. Thepolymers or resin system may be cross-linked by a variety of means suchas by peroxide agents, sulphur agents, radiation or other cross-linkingtechniques.

Any or all of the previously described components in the cores of thegolf balls of the present invention may be formed in such a manner, orhave suitable fillers added, so that their resulting density isdecreased or increased. For example, any of the components in the dualcores could be formed or otherwise produced to be light in weight. Forinstance, the components could be foamed, either separately or in-situ.Related to this, a foamed light weight filler agent may be added. Incontrast, any of these components could be mixed with, or otherwisereceive, various high density filler agents or other weightingcomponents such as relatively high density fibers or particulate agentsin order to increase their mass or weight.

The following commercially available thermoplastic resins areparticularly preferred for use in the noted dual cores employed in thegolf balls of the present invention: Capron 8351 (available from AlliedSignal Plastics), Lexan ML5776 (from General Electric), Pebax 3533 (apolyether block amide from Elf Atochem), and Hytrel G4074 (from DuPont).Properties of these four preferred thermoplastics are set forth below inTables 10-13. When forming a golf ball in accordance with the presentinvention, if the interior center component of the dual core is tocomprise a thermoplastic material, it is most preferred to utilize Pebaxthermoplastic resin.

TABLE 10 CAPRON 8351 DAM 50% RH ASTM Test MECHANICAL Tensile Strength,Yield, 7,800 (54) — D-638 psi (MPa) Flexural Strength, 9,500 (65) —D-790 psi (MPa) Flexural Modulus, 230,000 (1,585) — D-790 psi (MPa)Ultimate Elongation, % 200 — D-638 Notched Izod Impact, No Break — D-256ft-lbs/in (J/M) Drop Weight Impact, 150 (200) —  D-3029 ft-lbs (J) DropWeight Impact, 150 (200) —  D-3029 @ −40° F., ft-lbs (J) PHYSICALSpecific Gravity 1.07 — D-792 THERMAL Melting Point, ° F. (° C.) 420(215) — D-789 Heat Deflection 140 (60) — D-648 @ 264 psi ° F. (° C.)

TABLE 11 Lexan ML5776 TYPICAL PROPERTY DATA UNIT METHOD MECHANICALTensile Strength, yield, 8500 psi ASTM D 638 Type I, 0.125″ TensileStrength, break, 9500 psi ASTM D 638 Type I, 0.125″ Tensile Elongation,yield, 110.0 % ASTM D 638 Type I, 0.125″ Flexural Strength, yield, 12000psi ASTM D 790 0.125″ Flexural Modulus, 310000 psi ASTM D 790 0.125″IMPACT Izod Impact, unnotched, 60.0 ft - lb/in ASTM D 4812 73 F. IzodImpact, notched, 15.5 ft - lb/in ASTM 0 256 73 F. Izod Impact, notches,12.0 ft - lb/in ASTM D 256 73 F., 0.250″ Instrumented Impact 48.0 ft -lbs ASTM D 3763 Energy @ Peak, 73 F. THERMAL HDT, 264 psi, 0.250″, 257deg F. ASTM D 648 unannealed Thermal Index, 80 deg C. UL 7468 Elec PropThermal Index, 80 deg C. UL 7468 Mech Prop with impact Thermal Index, 80deg C. UL 7468 Mech Prop without impact PHYSICAL Specific Gravity, solid1.19 — ASTM D 792 Water Absorption, 0.150 % ASTM D 570 24 hours @ 73 F.Mold Shrinkage, 5.7 in/in E-3 ASTM D 955 flow, 0.125″ Melt Flow Rate,nom'l, 7.5 g/10 min ASTM D 1238 300 C./1.2 kgf (0) FLAME CHARACTERISTICSUL File Number, USA E121562 — — 94HB Rated 0.060 inch UL 94 (testedthickness)

TABLE 12 PEBAX ® 3533 RESIN ASTM TEST PROPERTY METHOD UNITS 3533Specific Gravity D792 Water Absorption 0.5 Equilibrium (20° C., 50%R.H.>) 24 Hr. Immersion D570 1.2 Hardness D2240 35D Tensile Strength,D638 psi 5600 Ultimate Elongation, Ultimate D638 % 580 Flexural ModulusD790 psi 2800 Izod Impact, Notched D256 ft-  20° C. lb./in. NB −40° C.NB Abrasion Resistance D1044 Mg/1000 104 H18/1000 g Cycles TearResistance Notched D624C lb./in. 260 Melting Point D3418 ° F. 306 VicatSoftening Point D1525 ° F. 165 HDT 66 psi D648 ° F. 115 Compression SetD395A % 54 (24 hr., 160° F.)

TABLE 13 HYTREL G4074 Thermoplastic Elastomer PHYSICAL Dens/Sp Gr ASTMD792 1.1800 sp gr 23/23C Melt Flow ASTM D1238 5.20 @ E - 190 C/2.16 kgg/10/min Wat Abs ASTM D570 2.100% MECHANICAL Elong@Brk ASTM D638 230.0%Flex Mod ASTM D790 9500 psi TnStr@Brk ASTM D638 2000 psi IMPACT NotchIzod ASTM D256 No Break @ 73.0 F. @ 0.2500 inft- lb/in 0.50 @ −40.0 F. @0.2500 inft-lb/in HARDNESS Shore ASTM D2240 40 Shore D THERMAL DTUL@66ASTM D648 122 F. Melt Point 338.0 F. Vicat Soft ASTM D1525 248 F. MeltPoint

The cores of the inventive golf balls typically have a coefficient ofrestitution of about 0.750 or more, more preferably 0.770 or more and aPGA compression of about 90 or less, and more preferably 70 or less. Thecores have a weight of 25-40 grams and preferably 30-40 grams. The corecan be compression molded from a slug of uncured or lightly curedelastomer composition comprising a high cis content polybutadiene and ametal salt of an α, β, ethylenically unsaturated carboxylic acid such aszinc mono- or diacrylate or methacrylate. To achieve higher coefficientsof restitution and/or to increase hardness in the core, the manufacturermay include a small amount of a metal oxide such as zinc oxide. Inaddition, larger amounts of metal oxide than are needed to achieve thedesired coefficient may be included in order to increase the core weightso that the finished ball more closely approaches the U.S.G.A. upperweight limit of 1.620 ounces. Non-limiting examples of other materialswhich may be used in the core composition including compatible rubbersor ionomers, and low molecular weight fatty acids such as stearic acid.Free radical initiator catalysts such as peroxides are admixed with thecore composition so that on the application of heat and pressure, acuring or cross-linking reaction takes place.

Wound cores are generally produced by winding a very long elastic threadaround a solid or liquid filled balloon center. The elastic thread iswound around the center to produce a finished core of about 1.4 to 1.6inches in diameter, generally. However, the preferred embodiment golfballs of the present invention preferably utilize a solid core, orrather a solid dual core configuration, as opposed to a wound core.

Method of Making Golf Balls

In preparing preferred embodiment golf balls in accordance with thepresent invention, a hard inner cover layer is molded (by injectionmolding or by compression molding) about a core (preferably a solidcore, and most preferably a dual core). A comparatively softer outerlayer is molded over the inner cover layer.

The dual cores of the present invention are preferably formed bycompression molding techniques. However, it is fully contemplated thatliquid injection molding or transfer molding techniques could beutilized.

For purposes of example, a preferred method of making the golf ball 45depicted in FIG. 4 is as follows. Specifically, a thermoset material,i.e. a core layer 42, is formed about an inner core component 40comprising a thermoplastic material as follows. Referring to FIG. 7,preforms 75 of a thermoset material, i.e. utilized to form the corelayer 42, are preheated in an oven for one-half hour at 170° F. andplaced in the bottom 73 of a molding assembly 70. A Teflon-coated plate76 with two hemispheres 77 and 78, each about 0.840 inches in diameter,is placed on top of the preforms. Additional preforms, preheated asdescribed above, are placed in the corresponding cavities of a top mold72. The bottom mold 73 is engaged with the top mold 72 and the assemblyflipped or otherwise inverted. The bottom one half of the mold assembly70 then becomes the top one half of the mold assembly. The mold assembly70 is then placed in a press and cold formed at room temperature usingapproximately 10 tons of pressure in a steam press. The molding assembly70 is closed for approximately two minutes and pressure released. Themolding assembly 70 is then opened and the Teflon plate 76 is removedthereby leaving one or more essentially perfectly formed one-half shellsor cavities in the thermoset material. Previously formed thermoplasticcore centers are then placed in the bottom cavities and the top portion72 of the molding assembly 70 is placed on the bottom 73 and thematerials disposed therebetween cured. The golf ball produced by thismethod had an inner core diameter of 0.840 inches in diameter. The outercore diameter had a final diameter of 1.470 inches, and a pre-molddiameter of 1.490 inches. A relatively hard inner cover layer is thenmolded about the resulting dual core component. The diameter of theinner cover was 1.570 inches. A comparatively softer outer cover layeris then molded about the inner cover layer. The outer cover diameter was1.680 inches. Details of molding the inner and outer covers are setforth below.

Four golf balls in accordance with the present invention were formed,each using a preferred and commercially available high melting pointthermoplastic material as an inner core component. Table 14, set forthbelow, summarizes these balls.

TABLE 14 Capron Lexan Pebax Hytrel Control 8351 ML 5776-7539 3533 G-4074(Single Core) Inner Core size (inches) 0.835 0.854 0.840 0.831 — weight(grams) 5.33 6.14 5.08 5.81 — rebound % (100″) 78 83 65 61 — Shore C(surface) — — 57 73 — Shore D (surface) 75 83 36 47 — Outer Core Cis 1,4Polybutadiene 100 100 100 100 100 Formulation Zinc oxide 27 26 28 21 25Zinc stearate 16 16 16 16 15 Zinc diacrylate 20 20 24 24 18 231 x L 0.90.9 0.9 0.9 0.9 163.9 162.9 168.9 161.9 158.9 Double Core size (inches)1.561 1.560 1.562 1.563 1.562 Properties weight (grams) 37.7 37.8 37.837.5 37.8 compression (riehle) 79 80 99 93 114 COR .689 .603 .756 .729.761 Molded Ball size (inches) 1.685 1.683 1.682 1.683 1.685 Propertiesweight (grams) 45.3 45.5 45.5 45.2 45.4 compression (riehle) 78 80 89 87102 COR .750 .667 .785 .761 .788 Cover Stock surlyn 8940 22 *T.G. MBIotek 7030 75.35 (used on all surlyn 9910 54.5 Unitane 0-110 23.9 aboveballs) surlyn 8320 10 Ultra Marine Blue 0.46 surlyn 8120 4 EastonbriteOB-1 0.26 T.B. MB* 9.5 Santonox R 0.038 100.0 100.00

Generally, the inner cover layer which is molded over the core, orpreferably a dual core component, is about 0.01 inches to about 0.10inches in thickness, preferably about 0.03-0.07 inches thick. The innerball which includes the core and inner cover layer preferably has adiameter in the range of 1.25 to 1.60 inches. The outer cover layer isabout 0.01 inches to about 0.10 inches in thickness. Together, the core,the inner cover layer and the outer cover layer combine to form a ballhaving a diameter of 1.680 inches or more, the minimum diameterpermitted by the rules of the United States Golf Association andweighing no more than 1.62 ounces.

Most preferably, the resulting golf balls in accordance with the presentinvention have the following dimensions:

Size Specifications: Preferred Most Preferred Inner Core Max. 1.250″1.00″  Min. 0.500″ 0.70″  Outer Core Max. 1.600″ 1.570″ Min. 1.500″1.550″ Cover Thickness (Total) Max. 0.090″ 0.065″ Min. 0.040″ 0.055″

In a particularly preferred embodiment of the invention, the golf ballhas a dimple pattern which provides coverage of 65% or more. The golfball typically is coated with a durable, abrasion-resistant, relativelynon-yellowing finish coat.

The various cover composition layers of the present invention may beproduced according to conventional melt blending procedures. Generally,the copolymer resins are blended in a Banbury type mixer, two-roll mill,or extruder prior to neutralization. After blending, neutralization thenoccurs in the melt or molten states in the Danbury mixer. Mixingproblems are minimal because preferably more than 75 wt %, and morepreferably at least 80 wt % of the ionic copolymers in the mixturecontain acrylate esters and, in this respect, most of the polymer chainsin the mixture are similar to each other. The blended composition isthen formed into slabs, pellets, etc., and maintained in such a stateuntil molding is desired. Alternatively, a simple dry blend of thepelletized or granulated resins which have previously been neutralizedto a desired extent and colored maslerbatch may be prepared and feddirectly into the injection molding machine where homogenization occursin the mixing section of the barrel prior to injection into the mold. Ifnecessary, further additives such as an inorganic filler, etc., may beadded and uniformly mixed before initiation of the molding process. Asimilar process is utilized to formulate the high acid ionomer resincompositions used to produce the inner cover layer. In one embodiment ofthe invention, a masterbatch of non-acrylate ester-containing ionomerwith pigments and other additives incorporated therein is mixed with theacrylate ester-containing copolymers in a ratio of about 1-7 weight %masterbatch and 93-99 weight % acrylate ester-containing copolymer.

The golf balls of the present invention can be produced by moldingprocesses which include but are not limited to those which are currentlywell known in the golf ball art. For example, the golf balls can beproduced by injection molding or compression molding the novel covercompositions around a wound or solid molded core to produce an innerball which typically has a diameter of about 1.50 to 1.67 inches. Thecore, preferably of a dual core configuration, may be formed aspreviously described. The outer layer is subsequently molded over theinner layer to produce a golf ball having a diameter of 1.620 inches ormore, preferably about 1.680 inches or more. Although either solid coresor wound cores can be used in the present invention, as a result oftheir lower cost and superior performance solid molded cores arepreferred over wound cores. The standards for both the minimum diameterand maximum weight of the balls are established by the United StatesGolf Association (U.S.G.A.).

In compression molding, the inner cover composition is formed viainjection at about 380° F. to about 450° F. into smooth surfacedhemispherical shells which are then positioned around the core in a moldhaving the desired inner cover thickness and subjected to compressionmolding at 200° to 300° F. for about 2 to 10 minutes, followed bycooling at 50° to 70° F. for about 2 to 7 minutes to fuse the shellstogether to form a unitary intermediate ball. In addition, theintermediate balls may be produced by injection molding wherein theinner cover layer is injected directly around the core placed at thecenter of an intermediate ball mold for a period of time in a moldtemperature of from 50° to about 100° F. Subsequently, the outer coverlayer is molded around the core and the inner layer by similarcompression or injection molding techniques to form a dimpled golf ballof a diameter of 1.680 inches or more.

After molding, the golf balls produced may undergo various furtherprocessing steps such as buffing, painting and marking as disclosed inU.S. Pat. No. 4,911,451.

The resulting golf ball produced from the hard inner layer and therelatively softer, low flexural modulus outer layer provide for animproved multi-layer golf ball having a unique dual core configurationwhich provides for desirable coefficient of restitution and durabilityproperties while at the same time offering the feel and spincharacteristics associated with soft balata and balata-like covers ofthe prior art.

The invention has been described with reference to the preferredembodiments. Obviously, modifications and alterations will occur toothers upon a reading and understanding the preceding detaileddescription. It is intended that the invention be construed as includingall such modifications and alterations in so far as they come within thescope of the appended claims or the equivalents thereof.

What is claimed:
 1. A golf ball comprising: a core having at least acenter component and a core layer disposed about said center component,wherein said core layer comprises more than one layer; and, a coverdisposed about said core; wherein said center component comprises athermoset material and said core layer comprises a thermoplasticmaterial; wherein said cover includes an outer cover layer having aShore D hardness of from about 40 to 55 and an inner cover layer havinga Shore D hardness of 60 or more, and wherein said outer cover layer issofter than said inner cover layer.
 2. The golf ball of claim 1 whereinsaid thermoset material comprises a material selected from the groupconsisting of (i) a diene-containing polymer, (ii) a metallocenecatalyzed polyolefin that is crosslinked, (iii) a polyurethane, (iv) asilicone, (v) a polyamide, (vi) a polyurea, and (vii) combinationsthereof; and said thermoplastic material comprises a material selectedfrom the group consisting of (i) an ionomer, (ii) a polyurethane, (iii)an elastomer, (iv) a polyetheramide, (v) a polyetherester, (vi) ametallocene catalyzed polyolefin, (vii) a styrene butadiene blockcopolymer, and (viii) combinations thereof.
 3. The golf ball of claim 1wherein said thermoset material comprises a polybutadiene rubber.
 4. Thegolf ball of claim 1 wherein said thermoset material comprises apolyurethane.
 5. The golf ball of claim 1 wherein said thermoplasticmaterial comprises a material selected from the group consisting of (i)polyurethane, (ii) polyester, (iii) polyamide, (iv) ionomer, (v)polycarbonate, (vi) polyether block amide, and (vii) combinationsthereof.
 6. The golf ball of claim 1 wherein said center component ofsaid dual core has an outer diameter of from about 0.500 inches to about1.250 inches, and said dual core has an outer diameter of from about1.25 to about 1.600 inches.
 7. The golf ball of claim 1 wherein at leastone of said core layers and said center component of said dual corecomprise a density increasing agent.
 8. The golf ball of claim 1 whereinat least one of said core layers and said center component of said dualcore comprise an agent that is foamed or otherwise reduced in density.9. A golf ball comprising: a core having at least a center component anda core layer disposed about said center component; and, a cover disposedabout said core; wherein said center component comprises a thermosetmaterial and said core layer comprises a thermoplastic material, whereinsaid thermoset material comprises a polyurethane; wherein said coverincludes an outer cover layer having a Shore D hardness of from about 40to 55 and an inner cover layer having a Shore D hardness of 60 or more,and wherein said outer cover layer is softer than said inner coverlayer.
 10. The golf ball of claim 9 wherein said thermoplastic materialcomprises a material selected from the group consisting of (i) anionomer, (ii) a polyurethane, (iii) an elastomer, (iv) a polyetheramide,(v) a polyetherester, (vi) a metallocene catalyzed polyolefin, (vii) astyrene butadiene block copolymer, and (viii) combinations thereof. 11.The golf ball of claim 9 wherein said thermoplastic material comprises amaterial selected from the group consisting of (i) polyurethane, (ii)polyester, (iii) polyamide, (iv) ionomer, (v) polycarbonate, (vi)polyether block amide, and (vii) combinations thereof.
 12. The golf ballof claim 9 wherein said center component of said dual core has an outerdiameter of from about 0.500 inches to about 1.250 inches, and said dualcore has an outer diameter of from about 1.25 to about 1.600 inches. 13.The golf ball of claim 9 wherein at least one of said core layer andsaid center component of said dual core comprise a density increasingagent.
 14. The golf ball of claim 9 wherein at least one of said corelayer and said center component of said dual core comprise an agent thatis foamed or otherwise reduced in density.
 15. The golf ball of claim 9wherein said core layer comprises more than one layer.